Use specific messages for const constructor with body.

pkg/dart_messages/lib/shared_messages.dart

Index: pkg/dart_messages/lib/shared_messages.dart
diff --git a/pkg/dart_messages/lib/shared_messages.dart b/pkg/dart_messages/lib/shared_messages.dart
index 5aa2cededb7a5963715c22b46f97fa240d8fe3e8..89a69bc217cc499042780f156105e35c1f8a45a1 100644
--- a/pkg/dart_messages/lib/shared_messages.dart
+++ b/pkg/dart_messages/lib/shared_messages.dart
@@ -191,37 +191,15 @@ final Map<String, Message> MESSAGES = {
         }
       ]),
 
-  // Const constructors (factory or not) may not have a body.
-  'CONST_CONSTRUCTOR_OR_FACTORY_WITH_BODY': new Message(
-      id: 'LGJGHW',
-      subId: 0,
-      categories: [Category.parserError],
-      template: "Const constructor or factory can't have a body.",
-      howToFix: "Remove the 'const' keyword or the body.",
-      usedBy: [dart2js],
-      examples: const [
-        r"""
-         class C {
-           const C() {}
-         }
-
-         main() => new C();""",
-        r"""
-         class C {
-           const factory C() {}
-         }
-
-         main() => new C();"""
-      ]),
   // Const constructors may not have a body.
   'CONST_CONSTRUCTOR_WITH_BODY': new Message(
       id: 'LGJGHW',
-      subId: 1,
+      subId: 0,
       specializationOf: "CONST_CONSTRUCTOR_OR_FACTORY_WITH_BODY",
       categories: [Category.parserError],
       template: "Const constructor can't have a body.",
       howToFix: "Try removing the 'const' keyword or the body.",
-      usedBy: [analyzer],
+      usedBy: [analyzer, dart2js],
       examples: const [
         r"""
          class C {
@@ -233,14 +211,14 @@ final Map<String, Message> MESSAGES = {
   // Const constructor factories may only redirect (and must not have a body).
   'CONST_FACTORY': new Message(
       id: 'LGJGHW',
-      subId: 2,
+      subId: 1,
       specializationOf: "CONST_CONSTRUCTOR_OR_FACTORY_WITH_BODY",
       categories: [Category.parserError],
       template: "Only redirecting factory constructors can be declared to "
           "be 'const'.",
       howToFix: "Try removing the 'const' keyword or replacing the body with "
           "'=' followed by a valid target.",
-      usedBy: [analyzer],
+      usedBy: [analyzer, dart2js],
       examples: const [
         r"""
          class C {